In these systems, a satellite positioning receiver aboard a mobile object provides position information in respect of the mobile object, obtained by triangulation on the basis of the navigation signals emitted by the satellites visible from the mobile object.
The receiver also receives data transmission signals which transmit complementary data to the satellite positioning receiver, so as to improve the services rendered to the users, for example, by improving the precision or the integrity of the positioning of the mobile object.
Among the data transmission signals may be cited the augmentation signals, arising from a GNSS augmentation system of the GBAS (“Ground-Based Augmentation System”) or SBAS (“Space-Based Augmentation System”) type, based on one or more ground stations, able to identify the errors in the information provided by satellites and to dispatch, to the satellite positioning receiver, augmentation signals transporting data representative of individual corrections on the signals emitted by the satellites. Satellite navigation systems comprising augmentation systems make it possible to provide position information of better precision and which is less impaired than that arising from satellite navigation systems devoid of augmentation systems.
Current data transmission signals are dispatched with a predetermined bitrate and a predetermined coding of the Viterbi type, which limit their performance. Typically, for a signal transmitted over 1 second, 500 symbols are dispatched, coded over 2 ms. The data are dispatched on a data pathway (symbol-modulated carrier of the data to be transmitted by the signal) but without any pilot pathway (non-message carrier pathway, not modulated by symbols), thereby limiting the capabilities for tracking these signals at the level of the receiver. Indeed, tracking is carried out more easily on a pilot pathway than on a data pathway since the energy of a pilot pathway can be accumulated in a coherent manner whereas on a data pathway this accumulation must be done in an incoherent manner thereby introducing an additional noise level.
One seeks to improve the quality of the services rendered by current satellite navigation systems while retaining compatibility with current services and developments, that is to say while using current receivers and signals.
Currently, to improve the services rendered to users, an improvement signal is dispatched to the receiver. However, the improvement signal is added to the existing data transmission signal within the limit of powers permitted by the regulations. The permitted power must therefore be shared between the various signals.
Currently, the improvement signal comprises:                either a data pathway, thereby making it possible to dispatch additional data to the receiver so as to provide new services to the users, but not making it possible to improve the tracking of the current data transmission signal,        or a pilot pathway and a data pathway, thereby reducing the tracking and decoding performance for the new data pathway since the power permitted by regulation is shared between the pilot pathway and the data pathway.        